1. Field of the Invention
The present invention relates to siren sound generators and siren sound detectors, especially for traffic signal pre-emption.
2. State of the Art
Siren sound generators (siren generators) and siren sound detectors (siren detectors), including siren detectors for traffic light pre-emption, are known. A particularly effective siren detector arrangement is disclosed in U.S. Pat. No. 4,864,297 to Shaw et al., incorporated herein by reference, in which a filter tuned to a mean precession frequency produces precession signals which are in turn filtered by "wail" and "yelp" low-pass filters, respectively. A similar arrangement is described in WO 95/24028, (McConnell et al.) published Sep. 8, 1995, incorporated herein by reference. The siren detector architecture described in McConnell et al., however, is DSP-(digital signal processor) based and is influenced by RF (radio frequency) design, allowing a great improvement to be achieved in the ability to detect siren signals having low signal to noise (SNR) ratios. In particular, the siren detector of McConnell et al. has been demonstrated effective in detecting siren signals down to about -2 to -3dB SNR. The sound technology disclosed in McConnell is referred to herein by the term FM Discriminator Receiver and is employed in the SONEM 2000 Digital Siren Detector made by the present assignee, Sonic Systems Ltd. of Vancouver, B.C.
The present invention relates to further improvements in siren detectors of the type described, as well as to siren generators, allowing for siren detection systems of greater flexibility and versatility.